1. Field of the Invention
The present invention is directed to a communication system having at least two communication subscribers exchanging data unidirectionally or bidirectionally.
2. Description of the Prior Art
The communication subscribers of such known communication systems are electrical devices that are respectively connected via network lines to a network termination for energy supply of the devices. The exchange of data between the communication subscribers usually occurs via separately implemented data and control lines that connect the individual devices of the communication system to one another. However, the devices also can be connected to a communication bus that connects the devices to one another.
Known are devices for internal house voice and data communication between at least two pieces of communication terminal equipment via a separate house power supply network. Energy is supplied to the communication terminal equipment via the power supply network, and an at least two-channel communication between the communication terminal equipment can simultaneously occur via the power supply network, wherein each piece of the communication terminal equipment always receives data via one of the two channels connecting the communication terminal equipment to one another and sends data via the other of the two channels.
DE 195 44 027 C2 discloses a bus system with bus subscribers that includes controls for communication with at least one other bus subscriber. A three-lead network cable is provided for connecting the bus subscribers to one another, as a result whereof the outlay for the cabling between the bus subscribers is reduced. However, a four-lead network cable is preferred, wherein the additional protective conductor serves as bus line. A single-channel communication between two bus subscribers connected to the bus line respectively occurs via the bus line.
DE 195 04 587 A1 also discloses a two-way communication system for energy supply networks for data transmission between a central device in the routing level of an electrical energy supply network and consumer devices.
The present invention is based on the object of implementing a communication system of the species initially cited such that the outlay for the connection of the communication subscribers for data exchange with one another is reduced, and such that the communication system is suitable for the transmission of data for triggering security-relevant functions at a communication subscriber.
This object is achieved by a communication system which include at least two communication subscribers unidirectionally or bidirectionally exchanging data with one another that are electrically connected to one another via at least one network cable which is, in turn, connectible to a terminal via which energy can be supplied to the communication subscribers and via which an at least two-channel transmission of data in the form of electrical signals occurs at the same time from a first to a second communication subscriber, wherein the communication subscribers include devices for generating signals to be transmitted via the network cable and/or for the interpretation of signals transmitted via the network cable. In the inventive communication system, thus, separately implemented data and control lines connecting the communication subscribers to one another for data exchange or, respectively, a separately implemented communication bus in the form of one or more bus lines to which the communication subscribers are connected is foregone.
On the contrary, a network cable that every communication subscriber already has for energy supply is also utilized for the transmission of data. In this way, the outlay for the connection of the communication subscribers of the communication system to one another is clearly reduced, since each communication subscriber that is to be accepted into the communication network only has to be connected to the network cable in order to be supplied with energy and in order to be able to exchange data with other communication subscribers. Here, too, the outlay for the preparation of a room in which a number of communication subscribers are intended to form such a communication system is advantageously reduced by the present invention since laying separate data and control lines or, respectively, bus lines of a separately implemented communication bus can be foregone.
A particular advantage of the present invention lies in the at least two-channel transmission of data via the network cable. The possibility of successive or simultaneous transmission of data via two separate transmission routes independent of one another in one of two selectable directions from one to another communication subscriber is particularly advantageous when triggering security-relevant functions at one of the communication subscribers, since such a triggering can be made dependent thereon that corresponding information is communicated to the corresponding communication subscribers via both transmission channels decoupled from one another. By way of example, let the triggering of x-radiation at an x-ray apparatus be cited.
One embodiment of the present invention provides that the network cable is an at least three-lead, shielded network cable connectible to a single-phase network terminal having a conductor, a zero conductor and a protective conductor. The shielded network cable enhances the security in the transmission of data, wherein the shielding reduces the superimposition of noise signals.
According to one version of the present invention, the conductor and the zero conductor form a first transmission channel via which a symmetrical transmission of data occurs, preferably with a high data rate. The carrier signal is thereby modulated with signals containing data upon transmission, wherein the modulated carrier signal is transmitted via the conductor and the zero conductor separately in the form of two signals. Upon reception, a difference signal to be demodulated and corresponding to the modulated carrier signal is acquired from the signals transmitted via the conductor and the zero conductor. The symmetrical transmission of data is distinguished by low susceptibility to disturbance since, after reception, a difference signal is acquired from the signals transmitted via the conductor and the zero conductor; the noise signals acting identically on the signals transmitted via the conductor as well as via the zero conductor being eliminated therefrom by the formation of the difference. The screened difference signal thereby corresponds to the modulated carrier signal that is to be demodulated for the recovery of the signals containing the data. The symmetrical transmission is preferably suitable for transmission of data with high data rates.
DE 41 38 065 A1, moreover, discloses a system for transmitting data and energy via a three-lead cable to which a number of subscribers are respectively connected with a transmission and reception unit, wherein the data transmission between the subscribers occurs with symmetrical signals on two of the three leads. A power supply unit for the subscribers which supplies a feed current onto the two leads of the cable in roughly equal parts is also connected to the cable.
According to another embodiment of the present invention, the protective conductor represents a second transmission channel in and of itself via which an asymmetrical transmission of data having, preferably, a low data rate occurs. The second transmission channel is decoupled from the first transmission channel and preferably serves as control line when triggering security-relevant functions of a communication subscriber. The carrier signal is modulated with signals containing data upon transmission and the modulated carrier signal is demodulated upon reception. The protection against noise signals derives with the cable shielding at the network in the case of the protective conductor.
According to another embodiment of the present invention, the network cable is an at least five-lead, shielded network cable connectible to a three-phase terminal having three conductors, a zero conductor and a protective conductor. The first and second conductor of the three conductors thereby form a first transmission channel, and the third of the three conductors and the zero conductor form a second transmission channel via which a symmetrical transmission of data respectively occurs, preferably with a high data rate. This provides that a carrier signal is respectively modulated with signals containing data upon transmission per transmission channel, the modulated carrier signal being separately transmitted via the two conductors of the respective transmission channel in the form of two signals. Upon reception, a difference signal to be demodulated and corresponding to the respectively modulated carrier signal is acquired via the signals transmitted over the two conductors of the respective transmission channel. In this way, a two-channel, symmetrical transmission of data is enabled, as a result whereof the amount of data transmittable between the two communication subscribers per time unit is clearly increased.
According to a further embodiment of the present invention, the protective conductor forms a third transmission channel via which an asymmetrical transmission of data occurs, preferably with a low data rate. The carrier signal is modulated with signals containing data upon transmission or, respectively, the modulated carrier signal is demodulated upon reception. In this way, a three-way channel transmission of data can be achieved with a five-lead, shielded network cable.
Additional embodiments contemplate that the data rates given symmetrical transmission preferably lie between the processor 1 through 100 Mbits/s, and the data rates given asymmetrical transmission preferably lie between approximately 9 and 200 kBit/s. The data rates for the symmetrical and the asymmetrical transmission, however, also can lie outside these ranges. The length of the transmission channel, i.e. the length of the network cable between the communication subscribers, can thereby amount to 100 m and more dependent on the type of network cable employed and the data rates to be transmitted.
Pursuant to another embodiment of the present invention, the device for generating and/or interpreting signals includes a filter circuit, at least one transformer [or: repeater] and a circuit for modulation of carrier signals with signals containing data or, respectively, for demodulation of modulated carrier signals. The filter circuit, which is preferably a passive LC filter, effects a separation of circuits upon transmission and reception of signals. The transformer serves the purpose of coupling the carrier signals modulated with signals containing data onto or, respectively, out of the conductors.
According to preferred embodiments of the present invention, the communication system includes a number of medical apparatus or components of a medical apparatus that form a medical work station. The inventive communication of the communication subscribers via the network cable thereby reduces the outlay required for the cabling of the medical apparatus to one another for data exchange to a considerable extent and also satisfies the demands made of security-critical apparatus in view of the triggering of security-relevant functions as a result of the at least two-channel transmission of data.